Low/zero VOC glycol ether-esters and use as clean-up solvents and paint thinners

This invention relates to low and zero VOC glycol ether-ester compositions suitable for use as clean-up solvents and paint thinners for solvent-borne resins and coatings. This invention particularly relates to a clean-up solvent and paint thinner for solvent-borne resins and coatings selected from compositions of Formula (I)

wherein R 1 is a C 1 -C 10 alkyl group, phenyl or benzyl, R 2 is either hydrogen or methyl, R 3 is a carbon chain including 4-6 carbon atoms, and n=2-4;

of Formula (II)

wherein R 1 and R 4 are, independently, C 1 -C 10 alkyl groups, phenyl or benzyl, R 2 is either hydrogen or methyl, R 3 is a carbon chain including 0-4 carbon atoms, and n=1-4; and mixtures thereof.

The invention also relates to a solvent-borne composition including a solvent-borne polymer and the low and zero VOC composition of the invention and a method for cleaning or thinning a solvent-borne composition.

Volatile organic compound (VOC) emissions contribute to the creation of ozone, a main constituent of smog. In the US, VOC regulations established by the US Environmental Protection Agency (EPA) and enforced at the state level dictate the maximum concentration of volatile solvents in paints, clean up solvents, and other products. In Europe, VOC limits are defined by the 2004/42/EC Solvents Directive for Decorative Paints. VOC regulations have become more and more stringent and have affected the use of mineral spirits, VMP naphtha, and other type of solvents commonly used to thin solvent-borne paints and to clean up paint from brushes, spray guns, paint lines, and other tools used in painting. Water, acetone, and t-butyl acetate are volatile solvents but they are exempt from VOC regulations as they do not contribute to smog generation. Water, however, is not an effective solvent for the removal of a variety of paints. Acetone and t-butyl acetate are effective solvents for this use but are highly flammable and their use may compromise worker safety.

U.S. Pat. No. 5,609,678 discloses certain propylene glycol ethers used in thinning oil-based resins and in cleaning equipment contaminated with oil-based resins. Glycol ether-ester compositions suitable for use as clean-up solvents and paint thinners for solvent-borne resins and coatings are not disclosed.

U.S. Patent Application Publication No. 20090198002A1 discloses coalescent compositions for aqueous coating compositions including blends of dibasic esters such as bis-glycol ether esters of C 4 -C 6 diacids specifically, succinic, glutaric, and adipic acids, with maximum boiling points of 400° C. Glycol ether-ester compositions suitable for use as clean-up solvents and paint thinners for solvent-borne resins and coatings are not disclosed.

The present invention serves to provide low or zero VOC compositions including certain glycol ether-esters that are suitable for use as clean-up solvents and thinners for solvent-borne compositions such as decorative and protective coatings for various substrates.

In a first aspect of the present invention there is provided a clean-up solvent and paint thinner for solvent-borne resins and coatings comprising a glycol ether-ester composition selected from the group of compositions of Formula (I)

wherein R 1 is a C 1 -C 10 alkyl group, phenyl or benzyl, R 2 is either hydrogen or methyl, R 3 is a carbon chain comprising 4-6 carbon atoms, and n=2-4;

of Formula (II)

wherein R 1 and R 4 are, independently, C 1 -C 10 alkyl groups, phenyl or benzyl, R 2 is either hydrogen or methyl, R 3 is a carbon chain comprising 0-4 carbon atoms, and n=1-4;

and mixtures thereof.

In a second aspect of the present invention there is provided a solvent-borne composition comprising said clean-up solvent and paint thinner of the first aspect of the present invention and a solvent-borne polymer.

In a third aspect of the present invention there is provided a method for cleaning or thinning a solvent-borne polymeric composition comprising contacting the solvent-borne polymeric composition with the clean-up solvent and paint thinner for solvent-borne resins and coatings composition of the first aspect of the present invention.

The present invention relates to a clean-up solvent and paint thinner for solvent-borne resins and coatings comprising a glycol ether-ester composition selected from the group of compositions of Formula (I)

wherein R 1 is a C 1 -C 10 alkyl group, phenyl or benzyl, R 2 is either hydrogen or methyl, R 3 is a carbon chain including 4-6 carbon atoms, and

n=2-4;

of Formula (II)

wherein R 1 and R 4 are, independently, C 1 -C 10 alkyl groups, phenyl or benzyl, R 2 is either hydrogen or methyl, R 3 is a carbon chain including 0-4 carbon atoms, and n=1-4; and mixtures thereof.

By “solvent-borne resin” herein is meant a resin, or polymer, dispersed in or dissolved in a medium including less than 10% by weight water (a “solvent”). By “solvent-borne composition” herein is meant a composition dispersed in or dissolved in a medium including less than 10% by weight water. By a “solvent-borne coating” herein is meant a fluid, partially dried, or dry pigmented or unpigmented coating or adhesive composition dispersed in or dissolved in, or capable of being dispersed in or dissolved in a medium including less than 10% by weight water. By “a clean-up solvent and paint thinner” is meant a medium capable of dissolving a solvent-borne resin or coating.

In each instance herein R3 is a carbon chain including a certain number of carbon atoms; the chain may be, for example, saturated, unsaturated, substituted, part of a ring structure, or combinations thereof. The individual carbon atoms in the chain may bear substituent groups such as, for example, —OH, —Cl, ═O, and the like.

Examples of glycol ether esters described by Formula I are diethylene glycol phenyl ether benzoate, dipropylene glycol phenyl ether levulinate, and tripropylene glycol n-butyl ether isopentanoate. Examples of bis-glycol ether esters described by Formula II are bis-dipropylene glycol n-butyl ether adipate, bis-diethylene glycol n-butyl ether malonate, bis-diethylene glycol n-butyl ether succinate, and bis-dipropylene glycol methyl ether maleate.

The glycol ether-esters of the present invention are esters of monocarboxylic acids or dicarboxylic acids and glycol ethers, the latter obtained by reacting alcohols or phenol with either ethylene oxide or propylene oxide. Any of several synthetic methods known to those skilled in the art can be used to prepare the aforementioned esters. For instance, stoichiometric amounts of the glycol ether and the desired carboxylic acid can be heated in the presence of a catalytic amount of a strong acid such as, for example, concentrated sulfuric acid and p-toluene sulfonic acid and a solvent such as, for example, heptane, and water removed azeotropically to yield the desired product. Another method of preparation employs the acid monochloride (or dichloride) instead of the carboxylic acid as a reactant. In this case, hydrogen chloride gas is given off instead of water during the reaction of the acid chloride with the glycol ether. The hydrogen chloride may be trapped using a water scrubber. Still another method of preparation involves the transesterification of a simple alkyl ester of the desired acid with a glycol ether in the presence of a titanium catalyst such as tetraisopropyl titanate. Still another method of esterification uses the acid anhydride as reactant in combination with the azeotropic removal of water. This method is aimed at producing diesters. Glycol ether esters obtained by any of the aforementioned methods can be purified by flash distillation under high vacuum.

The structural requirements of the glycol ether esters of the clean-up solvent and paint thinner for solvent-borne resins and coatings of the invention have been set forth in Formulas (I) and (II). The glycol ether esters are typically liquids in the 0-25° C. temperature range to facilitate their use as thinners and clean up solvents. These products are desirably less than 10% volatile by Method 24, preferably less than 5% volatile, and most preferably less than 1% volatile to be useful as low VOC solvents in the U.S. To be classified as VOC-exempt in the EU, the solvents must boil above 250° C. and preferably above 280° C.

Glycol ether monoesters described by Formula (I) were prepared from benzoic acid (or benzoyl chloride), ethyl levulinate, isopentanoic acid and valeric acid. Bis-glycol ether esters described by Formula (II) were prepared from malonic acid, succinic acid, maleic anhydride, and adipic acid (or adipoyl chloride). Glycol ethers used in these preparations were ethylene glycol n-hexyl ether, triethylene glycol n-hexyl ether, dipropylene glycol 2-ethylhexyl ether, diethylene glycol n-hexyl ether, diethylene glycol phenyl ether, diethylene glycol n-butyl ether, dipropylene glycol phenyl ether, tripropylene glycol n-pentyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, dipropylene glycol n-butyl ether, dipropylene glycol n-propyl ether, tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, tripropylene glycol n-butyl ether, triethylene glycol n-butyl ether, propylene glycol methyl ether, triethylene glycol n-pentyl ether, and ethylene glycol n-pentyl ether. Ethylene glycol phenyl ether and propylene glycol phenyl ether were used to prepare benzoates and succinates but the resulting glycol ether esters were solids melting in the 50-100° C. range which limits their utility as thinners and clean up solvents. The clean-up solvent and paint thinner for solvent-borne resins and coatings of the invention may include, in addition to the glycol ether-esters that can be used at a wide variety of concentrations ranging from 1 to 100%, by weight based on the weight of the clean-up solvent and paint thinner, other solvents commonly used in paint thinning and cleanup such as, for example, mineral spirits, alkanes, aromatic hydrocarbons, acetone, and esters such as alkyl acetates, propionates, benzoates, adipates, and phthalates.

The solvent-borne composition of the present invention includes the clean-up solvent and paint thinner of the invention and a solvent-borne polymer. Solvent-borne polymers include, for example, alkyds, styrenated alkyds, acrylic-modified alkyds, urethane polymers or prepolymers, uralkyds, epoxy resins, and the like. The solvent-borne composition may include pigments, extenders, and other coating adjuvants as are known in the coatings arts.

In the method for cleaning or thinning a solvent-borne polymeric composition of the present invention a solvent-borne polymeric composition is contacted with the clean-up solvent and paint thinner of the invention.

The invention in some of its embodiments will now be further described by reference to the following examples: